It depends on why you are saying the sentence. If you want to tell the story of HOW it was founded, use past tense. "This association was founded by my brother in 1998. He had been planning it for years, and when he finally got enough money, he quit his previous job and focused solely on bringing the foundation into being." If you are focusing on the effects of the foundation NOW, use present perfect. "In the past, there were never any organizations that helped professional clowns build saltwater aquariums, so circus workers who dreamed of working with reef-fish had to face their project's challenges alone and unsupported. Now, however, *this association has been founded by my brother,* and clowns everywhere have become empowered to follow their fishy dreams. Soon, every major city in this city will have at least one major aquarium curated by a clown." "In the past, my brother was always lazy and relaxed. Now, however, *he has founded an association*, and he is constantly working on improving it, so he is never able to relax."

@A☤P (Manu) Grazie.

Hi Ghia. 1) "IS / WAS founded" could be said for a building: "the buildings of Venice are/were founded upon wooden posts beaten inside the lagoon mud" The same idea can be extended to abstract entities: "The society is founded upon family" 2) "it was been founded" does not exist in English 3) We can choose between - HAD BEEN FOUNDED - HAS BEEN FOUNDED Would you like to say if the event A (= the foundation) has happened before or after an event B; and if the event B is in the Past or in the Present -- this will make the difference. An English speaker will explain it to you (I hope) Bye

@Natalia Спасибо.

... was founded in 20** (с указателем времени в прошлом без вариантов Past Simple) Без указания времени в прошлом можно употреблять Present Perfect, чтобы подчеркнуть результат в настоящем (она сейчас работает). Если я хочу сообщить о факте (кем была основана), я бы употребляла Past Simple.